Solder on a sloped surface

ABSTRACT

A method for depositing a solder layer or solder bump on a sloped surface. The method includes etching a sloped surface on a planar semiconductor substrate, depositing a solder-wettable layer on the sloped surface, masking the wettabler layer with a coating layer to control the position of the solder deposition, and using an organic film to prevent the solder from being deposited at regions not above either the wettable layer or the coating layer. Also, a semiconductor device structure on which a solder layer or solder bump is formed exclusively on a sloped surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.10/385,487 filed Mar. 12, 2003 now U.S. Pat. No. 6,764,937.

BACKGROUND

Solder is a material that typically contains tin and lead and that iscommonly used during the manufacturing of electronic circuit boards.Solder generally has a lower melting temperature than the metals thatmay be included, as lines or layers, in the circuit boards. Hence, oncetwo or more metal lines or layers have been formed in a circuit board,solder may be used to form an electrical contact between the layersand/or lines.

FIGS. 1A–1E show cross-sections of semiconductor device structures aftervarious steps of a process for depositing solder on a planarsemiconductor substrate surface have been performed according to therelated art. FIG. 1A is a cross-sectional view of a semiconductorsubstrate 100, such as silicon or gallium arsenide, and of an organicfilm 110, such as a photoresist film, that has been deposited on thesemiconductor substrate 100. The organic film 110, according to therelated art, is typically spun onto the substrate 100 and is typicallyin contact with the entire surface of the semiconductor substrate 100.

FIG. 1B is a cross-sectional view of the layers 100, 110 discussed aboveafter the organic film 110 has been selectively etched to form a seriesof holes 120 (or channels, troughs, grooves, or openings) above thesubstrate 100. The holes 120 in the organic film 110 may be formed viaphoto-lithography or by any other process known in the art ofsemiconductor device manufacturing.

FIG. 1C is a cross-sectional view of the substrate 100 and organic film110 discussed above after the holes 120 in the organic film 110 havebeen filled, at least partially, with solder paste 130. Solder paste, ingeneral, typically includes an admixture of flux and solder particles.The solder paste 130 shown in FIG. 1C may be deposited in the holes 120by any process known in the art. For example, a process similar to thestencil printing process used in the surface mount assembly process canbe used. Specifically, a squeegee can be used to “roll” a bead of solderpaste 130 across the organic film 110 to deposit the solder paste 130into the holes 120.

FIG. 1D is a cross-sectional view of the substrate 100 after the solderpaste 130 has been heat-treated to form solder bumps 140 on thesubstrate 100. In order to form the solder bumps 140, the temperature ofthe solder paste 130 that had been in the holes 120 of the organic film110 was raised. The higher temperature caused the flux portion that hadbeen in the paste 130 to liquefy and activate the metal surfaces andcaused the solder particles in the paste to melt. In the molten phase,the solder will wet to a solderable pad on the substrate surface whilethe surface tension of the liquid solder will cause the molten solder toform the shape of the solder bump. Upon cooling of the melted solderparticles, solid solder bumps 140 were formed. Typically, thetemperature of the solder paste 130 is raised by the use of an oven orhot plate.

FIG. 1E is a cross-sectional view of the substrate 100 and the solderbumps 140 after the organic film 110 has been removed. The organic film110 may be removed by any process that known in the art. Upon removal ofthe organic film 110, the substrate 100 may have additional structures,such as metal layers and metal lines, deposited thereon, and the solderbumps 140 can be used to electrically connect two or more metal layersor lines.

SUMMARY

A method of depositing solder, the method including the steps ofproviding a substrate that includes a substantially planar surface and asloped surface adjacent to the substantially planar surface, forming awettable layer on a portion of the sloped surface, and forming a solderlayer on a first portion of the wettable layer.

A semiconductor device including a substrate having a substantiallyplanar surface and an interior sloped surface, a wettable layer adheredto a portion of the interior sloped surface, and a solder layer adheredto a first portion of the wettable layer.

DESCRIPTION OF THE DRAWINGS

The detailed description will refer to the following drawings, whereinlike numerals refer to like elements, and wherein:

FIGS. 1A–E show the steps of a process for depositing solder on a planarsurface according to the related art; and

FIGS. 2A–I illustrate steps of a process for depositing solder on asloped surface.

DETAILED DESCRIPTION

The following detailed description is presented to enable any personskilled in the art to make and use devices that include solder. Forpurposes of explanation, specific nomenclature is set forth to provide athorough understanding of making and using such devices. However, itwill be apparent to one skilled in the art that these specific detailsare not required to make and use the devices. Descriptions of specificapplications are provided only as representative examples. Variousmodifications will be readily apparent to one skilled in the art, andthe general principles defined herein may be applied to otherembodiments and applications without departing from the spirit and scopeof the methods and devices described herein. The methods and devices arenot intended to be limited to the embodiments shown, but are to beaccorded the widest possible scope consistent with the principles andfeatures disclosed herein.

Historically, solder bumps have been deposited exclusively onsubstantially planar surfaces, such as the surface of the substrate 100shown in FIGS. 1A–E and discussed in detail above. However, solder bumpshave generally not been deposited on sloped surfaces. Sincesemiconductor devices typically include both substantially planar andsloped surfaces, the need exists for methods to deposit solder on sloped(i.e., non-planar) surfaces. FIGS. 2A–I illustrate various embodimentsof methods of depositing solder and solder bumps on sloped surfaces.

With reference now to FIG. 2A of the Drawings, there is illustrated across-sectional view of a substrate 200 that includes two substantiallyplanar surfaces 210 and two sloped surfaces 220. In some cases, the twosloped surfaces 220 may be on opposite sides of the same square hole orrectangular channel formed in the substrate 200, as is well understoodin the art. As shown, each of the sloped surfaces 220 may be positionedadjacent to a substantially planar surface 210 of the substrate 200. Theslope of the sloped surfaces 220 relative to the planar surface 210 maybe at any angle greater than 0° and less than 90°, measured relative toa line extending horizontally from the planar surface 210. However, the5°, 10°, 20°, 30°, 45°, 60°, 70°, and 80° angles, plus or minus 2.5°,are preferred in certain embodiments.

The sloped surfaces 220 may be formed by etching the substrate 200. Theetching step that forms the sloped surfaces 220 may includeanisotropically etching completely through the substrate 200 to form ahole. Alternately, the etching step may form a channel in the substrate200 and/or may not etch completely through the substrate 200.

FIG. 2B is a cross-sectional view of the substrate 200 shown in FIG. 2Aand of a wettable layer 230 that has been formed on a portion of one ofthe sloped surfaces 220 of the substrate 200. The wettable layer 230 mayinclude a metal that is wettable by solder (i.e., a metal on whichsolder can spread evenly, as opposed to beading up on). The wettablelayer 230 may be formed by any process known in the art including, butnot limited to, evaporation, sputtering, and plasma deposition. Metalsthat may be included in the wettable layer 230 include, but are notlimited to, gold, silver, and copper. Compounds that are solder-wettablemay also be used.

As shown in FIG. 2B, the wettable layer 230 may be formed partially onthe sloped surface 220 and partially on the planar surface 210 of thesubstrate 200. In this case, the portion of the wettable layer 230 thatis formed on the planar surface 210 of the substrate 200 may besubstantially planar. Alternately, the wettable layer 230 may bedeposited exclusively on the sloped surfaces 220. The benefits offorming a portion of the wettable layer 230 on the planar surface 210will become apparent from the discussion below, as will the benefits offorming the wettable layer 230 exclusively on the sloped surface 220.

FIG. 2C is a cross-sectional view of the substrate 200 and wettablelayer 230 discussed above, after a coating layer 240 has been formed ona portion of the wettable layer 230 and of the substrate 200. Thecoating layer 240 may include one or more dielectric materials that arenot solder-wettable. Such materials include, but are not limited to,oxides, polyimides and solder masks. The coating layer 240 may be formedby any method known in the art and may be thought of as a mask for thewettable layer 230 during solder deposition, as will be seen below.

FIG. 2D is a cross-sectional view of the structure shown in FIG. 2Cafter an organic film 250 or organic layer has been adhered to a portionof the substantially planar surface 210 of the substrate 200. Theorganic film 250 or layer may or may not be adhered to the wettablelayer 230 or the coating layer 240, but may be in contact with both thewettable layer 230 and the coating layer 240. According to certainembodiments of the methods for solder-deposition discussed herein, theorganic film 250 is not in contact with the sloped surfaces 220 of thesubstrate 200. Rather, the organic film 250 forms a bridge over thesloped surfaces 220 and over any hole or cavity that has been etched orotherwise formed in the substrate 200.

A convenient method for substantially preventing the organic film 250from adhering to or contacting the sloped surfaces 220 of the substrate200 involves using a rigid or semi-rigid and substantially planar sheetof material as the organic film 250. The sheet may be adhered to thesubstantially planar surfaces 210 of the substrate 200 after thewettable layer 230 and the coating layer 240 have been formed. Then,because of the inherent rigidity of the substantially planar sheet, theorganic film 250 will not dip into the etched portion of the substrate200 and will therefore not contact the sloped surfaces 220, as shown inFIG. 2D.

No limitations are made on the materials that may be included in theorganic film 250. However, polymers that can form thin sheets withenough rigidity to bridge the etched portion of the substrate 200 arepreferred. The organic film 250 may be fixed or held in place relativeto the substrate 200 via electrostatic forces, a chemical adhesive,and/or mechanical forces. For example, the organic film 250 may berolled out over the substrate 200 or may be wrapped around the substrate200 like plastic food wrap around a plate.

FIG. 2E is a cross-sectional view of the structure shown in FIG. 2Dafter a section of the organic film 250 has been removed, leaving anempty volume 255 above portions of the wettable layer 230 and coatinglayer 240. The removed section of the organic film 250 is divided intotwo portions to facilitate description. The first portion of the removedsection, designated by the reference numeral 256, is positioned aboveone of the planar surfaces 210 of the substrate 200 and contacts aplanar portion of the wettable layer 230 before removal. In FIG. 2D, thefirst portion 256 is supported from underneath by the substrate 200, thewettable layer 230, and the coating layer 240. The second portion of theremoved section, designated by the reference numeral 257, is positionedabove the etched portion of the substrate 200 before removal and is notsupported by the substrate 200. Instead, the second portion 257 of theremoved section is bridging the etched portion of the substrate 200.

Subsequent to the removal of the second portion 257, as shown in FIG.2E, the remaining organic film 250 retains its substantially planarshape and continues to bridge across the etched portion of the substrate200. In other words, the organic film 250 does not dip or droop into theetched portion of the substrate 200 and does not contact the slopedsurface 220. Hence, a gap 260 or unfilled space is formed between theorganic film 250 and the wettable layer 230. As shown in FIG. 2E, thegap 260 is formed adjacent to one of the sloped surfaces 220 of thesubstrate 200.

FIG. 2F is a top view of the structure illustrated in FIG. 2E. In thisembodiment, the removed section of the organic film 250, represented bythe empty volume 255, has a rectangular shape and a width that isslightly larger than the width of the wettable layer 230 and the coatinglayer 240. Accordingly, the substrate 200 is exposed on both sides ofthe wettable layer 230 and the coating layer 240.

FIG. 2G is a cross-sectional view of the structure illustrated in FIGS.2E and 2F, after the empty volume 255 has been substantially filled withsolder paste 270. The solder paste 270 may be placed in the volume 255by any means known in the art of semiconductor device manufacturing anddoes not have to exactly fill the entire volume 255. Any solder pastethat is deposited on the organic film 250 may, optionally, be removedafter the volume 255 has been substantially filled. Typically, thesolder paste 270 is viscous enough and the gap 260 is small enough suchthat little or none of the solder paste 270 flows through the gap 260until the solder paste 270 is heated.

FIG. 2H is a cross-sectional view of the structure shown in FIG. 2Gafter the solder paste 270 has been heated and processed to form asolder layer 280 on at least a portion of the wettable layer 230. Thesolder layer 280 may be formed on a portion of or all of the wettablelayer 230 that is not covered by the coating layer 240. The solder layer280 may be formed by thermally treating the solder paste 270 in such away that the flux in the paste 270 liquifies and activates the metalsurfaces and the solder particles in the paste melt together to form thedenser solder layer 280. According to certain embodiments of methods fordepositing solder, the solder layer 280 may be formed by heating thesolder paste 270 to about 180° C. or less, plus or minus approximately5° C. Although a solder layer 280 is shown in FIG. 2G, solder bumps mayalso be formed if more solder paste 270 is used, as is understood in theart.

FIG. 2I is a cross-sectional view of the structure shown on theleft-hand side of FIG. 2H after the organic film 250 has been removed.The organic film 250 may be removed by any method known in the art suchas, but not limited to, chemical dissolution, heating, and applicationof mechanical force to cause de-lamination.

The structure shown in FIG. 2I includes a substrate 200 having asubstantially planar surface 210 and an interior sloped surface 220.Also included is a wettable layer 230, which may include a metal, andthat is adhered to a portion of the interior sloped surface. Accordingto alternate structures, the entire wettable layer 230 may be adhered tothe sloped surface 220, if desired.

Adhered to a portion of the wettable layer 230 is the solder layer 280.In FIG. 2I, the solder layer 280 is positioned over both a portion ofthe sloped surface 220 and a portion of the planar surface 210. However,according to alternate structures, the solder layer 280 may be formedand/or positioned exclusively over all or a portion of the slopedsurface 220. When the wettable layer 230 is formed over a portion of theplanar surface 210, the wettable layer may be used to provide anelectrical contact to a line or layer formed on the planar surface 210.

As illustrated in FIG. 2I, a coating layer 240 adheres to a portion ofthe wettable layer 230. The coating layer 240, during the manufacturingof the structure shown in FIG. 2I, can assist in preventing depositionof the solder layer 280 in undesired locations by effectively maskingthe wettable layer 230. Once the solder layer 280 has been formed, thecoating layer 240 may, optionally, be removed from the structure tofacilitate the formation of electrical connections to lines and/orlayers on the adjacent planar surface 210.

The coating layer 240 may include any material that is not wettable bysolder (i.e., on which solder does not readily spread). For example, thecoating layer 240 may include a dielectric material or, morespecifically, an oxide. The solder layer 280 may, among other materials,include a tin-bismuth compound or a eutectic, tin-lead compound.However, no particular restrictions are placed on the materials that maybe used to build the structure illustrated in FIG. 2I.

While the aforementioned and illustrated methods for forming a solder ona sloped surface have been described in connection with exemplaryembodiments, those skilled in the art will understand that manymodifications in light of these teachings are possible, and thisapplication is intended to cover any variation thereof.

1. A semiconductor device comprising: a substrate having a substantially planar surface and an interior sloped surface; a wettable layer directly adhered to a portion of the interior sloped surface; and a solder layer adhered to a first portion of the wettable layer.
 2. The semiconductor device of claim 1, wherein the wettable layer comprises a metal.
 3. The semiconductor device of claim 1, wherein the solder layer comprises a tin-bismuth compound.
 4. The semiconductor device of claim 1, wherein the solder layer comprises a eutectic tin-lead compound.
 5. The semiconductor device of claim 1, wherein the wettable layer is adhered to a section of the substrate, further wherein the wettable layer extends from a first portion of the substantially planar surface to the portion of the interior sloped surface.
 6. The semiconductor device of claim 1, wherein the length of the wettable layer is shorter than a length of the interior sloped surface.
 7. A semiconductor device comprising: a substrate having a substantially planar surface and an interior sloped surface; a wettable layer adhered to a portion of the interior sloped surface; a solder layer adhered to a first portion of the wettable layer; and a coating layer adhered to a second portion of the wettable layer.
 8. The semiconductor device of claim 7, wherein the coating layer is a non-wettable layer.
 9. The semiconductor device of claim 8, wherein the coating layer comprises a dielectric material.
 10. The semiconductor device of claim 7, wherein the wettable layer is adhered to a section of the substrate, further wherein the wettable layer extends from a first portion of the substantially planar surface to the portion of the interior sloped surface.
 11. The semiconductor device of claim 7, wherein the length of the wettable layer is shorter than a length of the interior sloped surface.
 12. A semiconductor device comprising: a substrate having a substantially planar surface and an interior sloped surface; a wettable layer adhered to a portion of the interior sloped surface; a solder layer adhered to a first portion of the wettable layer; and a rigid organic film adhered to a portion of the substantially planar surface of the substrate and adjacent to a portion of the sloped surface.
 13. The semiconductor device of claim 12, wherein the wettable layer is adhered to a section of the substrate, further wherein the wettable layer extends from a first portion of the substantially planar surface to the portion of the interior sloped surface.
 14. The semiconductor device of claim 12, wherein the length of the wettable layer is shorter than a length of the interior sloped surface. 